1. Field of the Invention
The present invention relates to a switching device for use with sea rescue systems such as a radio buoy, radar transponder (SART) and emergency position report radio beacon (EPIRB) which uses a satellite.
2. Description of the related art
As well known, the sea rescue systems must meet standards provided by IMO (International Marine Affairs Organization), ITU (International Tele-communication Union) and the like. In addition, they must satisfy various kinds of regulations provided by Classification Societies. Those technical provisions, which are associated with the switching device, of these standards and regulations include the following sentences in addition to the common provisions.
(1) Its machinery and tools shall be reliable under any extreme conditions.
(2) It shall be provided with appropriate means for preventing it from being mistakenly made operative.
(3) It shall have such a water-tight arrangement as to be durable for five minutes at a depth of 10 m in the sea (its electric circuit shall be durable against destructive influences caused by freeze and water leakage).
(4) It shall be automatically operated.
(5) It shall be manually operated and stopped (It may be so through remote control).
(6) It shall be easily tested (without transmitting signals).
(7) It shall not be damaged even when it is dropped from the height of 20 m into the sea.
(8) While it is on board, it shall be normally operated even if shock and vibration usually added to the decks of navigating ships exceed a certain range.
The mercury switch (or inverted switch) can be cited as the switching mechanism which is often used with the conventional systems under the above-mentioned conditions. This mercury switch used mercury contacts and when the system is turned right side up on the sea or in its container, the mercury switch is closed to automatically start the system. When it is to be stopped, the system is turned upside down. In other words, the system is housed upside down in the container.
When the system is set like this, however, the following problems are caused.
(1) It is likely to be led to malfunction by forces such as shock, vibration and shake applied from outside.
(2) It cannot be easily tested (or operated) (by one touch of finger).
(3) It is likely to be mistakenly operated.
This is because the system must be set upside down because of the structure of the mercury switch in the case of the switching device for use with the conventional sea rescue systems.